In order to be able to effectively test, rehabilitate and exercise a person's back musculature involved in trunk extension/flexion motion, it is important to prevent motion by muscle groups other than the back musculature which performs the trunk extension/flexion motion. Specifically, if the legs are not stabilized, it is impossible to determine the range of motion traversed by the trunk in the trunk extension/flexion motion. Also, if the legs are free to move during the trunk extension/flexion test, rehabilitation or exercise procedure, an appreciable amount of force could be produced by the lower body in the movement, making it impossible to measure in isolation the strength of the trunk musculature in the trunk extension/flexion motion.
Presently, leg straps are used for leg stabilization on trunk extension/flexion machines. These leg straps have proved to be unacceptable for a number of reasons. First, leg straps are not rigid enough to provide the degree of stabilization required. Also, leg straps are not comfortable for the person, and such discomfort will discourage the person from exerting the maximum trunk extension/flexion force possible and also will discourage the person from extending or flexing the trunk to the full range of motion. Stabilization using leg straps has the additional disadvantage of not being able to be easily and quickly accomplished. Further, the stabilization of the legs by leg straps is not reproducible in that the stabilization provided by leg straps differs from procedure to procedure, making it virtually impossible to make comparative measurements of a person's trunk musculature strength and trunk extension/flexion range of motion from one procedure to another.